gulpfile.config.json

{
    "scripts": {
        "sourceFiles": ["!layout/scripts/**/_*.js", "layout/scripts/**/*.js"],
        "targetFilename": "app.js",
        "targetFolder": "web/layout"
    },
    "images": {
        "sourceFiles": ["layout/images/**/*"],
        "targetFolder": "web/layout/images"
    },
    "styles": {
        "sourceFiles": ["!layout/styles/**/_*.scss", "layout/styles/**/*.scss", "layout/styles/**/*.css"],
        "targetFolder": "web/layout",
        "cleanCss": {
            "level": {
                "1": {
                    "all": true,
                    "roundingPrecision": 5
                },
                "2": {
                    "all": false,
                    "mergeAdjacentRules" : true,
                    "mergeNonAdjacentRules" : true,
                    "mergeMedia": true,
                    "reduceNonAdjacent": true,
                    "removeDuplicates": true,
                    "removeEmpty": true
                }
            }
        }
    }
}